Method for manufacturing an active fixation electrode

ABSTRACT

The present invention relates to methods for manufacturing active fixation helices for the stimulation and/or sensing of organs. A first embodiment of a method in accordance with the present invention for making a helix comprises a first step of producing an elongated helix precursor body comprising one or more electrical conductors surrounded by an insulating material. This helix precursor body is then shaped into a helix, material removed in predetermined places in order to expose the areas of the conductors which will be used as electrodes in the final product. The body is coated with an electrically conducting biocompatible coating which is subsequently partly removed in continuous loops from around the electrodes in order to electrically insulate them from each other and to ensure that the electrically active areas of the electrodes are of the correct dimensions.

FIELD OF THE INVENTION

This application is a division of U.S. patent application Ser. No.12/522,001, filed Jul. 2, 2009, which claims priority from InternationalApp. No. PCT/SE2007/000084, filed Jan. 31, 2007.

FIELD OF THE INVENTION

The present invention relates to methods for manufacturing activefixation electrodes for electrical medical leads, in particularly helixelectrodes intended to be screwed into body tissue.

BACKGROUND OF THE INVENTION

Implantable medical electrical stimulation and/or sensing leads (alsocalled “leads” or “electrode leads”) are well known in the fields oftissue and organ stimulation and monitoring. Such fields include cardiacpacing. Leads may be attached to an organ by an active fixation meanswhich is designed to penetrate the surface of the organ that is to bestimulated or sensed. A common active fixation means employs a helixwhich has a sharpened tip and is mounted at the end of the electrodelead. The fixation helix typically has an outside helix diameter whichis slightly less than that of the lead body and extends in axialalignment with the lead body. The sharpened tip of the helix can bescrewed into the organ by being rotated. Typically the helix iselectrically connected to one or more conductors in the electrode lead.These conductors can be electrically connected to one or more exposedsurfaces of the helix which then can be used as stimulating and/orsensing electrodes. A fixation helix therefore may contain one or aplurality of conductors. Typically the outer surface of the helix,including the exposed surfaces used as electrodes, is partly coveredwith a biocompatible coating to minimise interference with the tissue towhich it is to be attached. Typically the biocompatible coating iselectrically conducting and it is arranged in a predetermined patternwith continuous gaps on the insulating material around the exposedelectrode surfaces in order to prevent the different electrodes frombeing in electrical contact with each other. The sizes of the surfaceareas of the exposed electrodes are set at levels which are compatiblewith the organ they are attached to. US Patent Application US2006/0122682 describes an active fixation helix for an electricalmedical leads and methods of making such active fixation helixes.

SUMMARY OF THE INVENTION

The present invention relates methods for manufacturing active helicessuitable for use as active fixation electrodes for electrical medicalleads, in particularly helix electrodes intended to be screwed into bodytissue. Such helices are made of thin electrical conductors, encased inan insulating material—usually treated to be biocompatible, and twistedinto the shape of a helix. The portions of the conductors are exposed toform electrically active surfaces which can be used for stimulating orsensing.

A first embodiment of a method in accordance with the present inventionfor making a helix comprises a first step of producing an elongatedhelix precursor body comprising one or more electrical conductorssurround by an insulating material. This helix precursor body is thenshaped into a helix, material removed in predetermined places in orderto expose the areas of the conductors which will be used as electrodesin the final product and coated with an electrically conductingbiocompatible coating which is subsequently partly removed in continuousloops from around the electrodes in order to electrically insulate themfrom each other and to ensure that the electrically active areas of theelectrodes are of the correct dimensions.

An alternative embodiment of a method in accordance with the presentinvention for making a helix comprises a first step of producing anelongated helix precursor body comprising one of more electricalconductors surrounded by an insulating material. Material is thenremoved at predetermined places from the helix precursor body in orderto expose the areas of the conductors which will be used as electrodesin the final product. The body is coated with an electrically conductingbiocompatible coating which is then removed in continuous loops fromaround the electrodes in order to electrically insulate them from eachother and to ensure that the electrically active areas of the electrodesare of the correct dimensions. The body is then formed in to the shapeof a helix.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. As will be realized, theinvention is capable of modifications in various aspects, all withoutdeparting from the spirit and scope of the present invention.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

DESCRIPTION OF THE FIGURES

FIG. 1 shows schematically an example of an electrical medical leadprovided with an active fixation means;

FIG. 2 shows schematically an embodiment of electrically active helixhaving a single conductor;

FIG. 3 shows schematically an embodiment of a multi-conductorelectrically active helix;

FIGS. 4 a)-4 e) show schematically steps in a first method in accordancewith the present invention for making an active fixation means;

FIGS. 5 a)-5 f) show schematically stages in the manufacture of amulti-conductor helix precursor body;

FIGS. 6 a)-6 e) show schematically steps in a second method inaccordance with the present invention for making an active fixationmeans; and

FIGS. 7 a)-7 c) show schematically cross-sections through examples ofpossible helix precursor bodies.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically an example of an electrical medical lead 1provided with an active fixation means 3. The active fixation means isformed by an electrically active helix 5 having a proximal end 7 inelectrical connection with a conductor (not shown) inside saidelectrical medical lead 1 and a sharpened distal end 9. A plurality ofhelix revolutions 11 are arranged between said proximal end 7 and saiddistal end 9. The helix 5 is attached to the lead 1 by a sleeve 12 whichsurrounds the end of the lead and one or more revolutions 11 of thehelix 5.

FIG. 2 shows schematically an embodiment of electrically active helixhaving a single conductor. The helix body 13 surrounds a longitudinallyextending lumen 15 and is comprised of an electrically conducting core17 which is at least partially surrounded by an insulating sheath 21such that a continuous portion of the surface 23 said electricallyconducting core 17 is exposed. The exposed surface 23 is coated with anelectrically conducting biocompatible coating 27 and preferably theinsulating sheath is also covered with a biocompatible coating. In orderto electrically insulate the exposed surface 23 of the core 17 from therest of the surface of the helix body, a continuous loop of the surfaceof the helix surrounding said exposed surface 17 must be free ofelectrically conducting material.

FIG. 3 shows schematically an embodiment of a multi-conductorelectrically active helix. The helix body 33 surrounds a longitudinallyextending lumen 35 and is comprised of electrically conducting cores 37,39 each of which is at least partially surrounded by an insulatingsheath 41 such that a continuous portion of the surface 43, respectively45, of each said electrically conducting core 37, 39 is exposed. Eachexposed surface 43, 45 of the cores and the insulating sheath 41 iscoated with an electrically conducting biocompatible coating 47 but theexposed surfaces 43, 45 are electrically insulated from each other andthe sheath 41 by being surrounded by a continuous loop of insulatingmaterial. This is described in more detail below.

A first embodiment of a method for producing an active fixation means inthe form of a multi-conductor electrically active helix will now bedescribed in connection with FIGS. 4 a)-4 e). In a first step anelongated cylindrical helix body precursor 51 is formed. This helix bodyprecursor 51 has a proximal end 53 and a distal end 55 and comprisesfirst and second elongated electrically conducting cores 37, resp. 39,surrounded by a sheath 41 of insulating material 42. The cores 37, 39can be made of any suitable conducting material, for example a metalsuch as platinum.

An example of such a helix body precursor 51 is shown in FIG. 4 a). Inthis example the first core 37 is arranged along the centrallongitudinal axis of the helix body precursor 51 and the second core 39is arranged parallel to the first core 37 and between the first core 37and the outer surface 57 of the helix body precursor. This can beachieved for example by co-extruding the cores 37, 39 inside aninsulating sheath material.

In the next step of the method a predetermined length of second core 39and the insulating material surrounding it are removed from distal end55, leaving a shoulder 58 in the helix body precursor 51, said shoulderextending over a portion of the first core 37 which is still surroundedby insulating material 42 as shown in FIG. 4 b).

In a third step, as shown in FIG. 4 c) shoulders 59, resp. 61, areformed in the insulating sheath 41 by selectively removing insulatingmaterial from the distal end 55 of the helix body precursor 51 in orderto expose resp. a surface 43 of the first electrically conducting core37, and a surface 45 of the second electrically conducting core 39. Inthis example shoulder 59 is a continuation of shoulder 58 in a directiontowards the first electrically conducting core 37 but it is conceivableto place shoulder 59 further away from the distal end 55 than shoulder58, thereby removing or undercutting shoulder 58. In this embodiment ofthe present invention part of exposed first core 37 nearest the distalend 55 of the helix body precursor 51 is levelled so that the exposedsurface 43 is coplanar with the longitudinally extending surface 62 ofshoulder 59. Similarly part of exposed second core 39 nearest the distalend 55 of the helix body precursor 51 is removed so that its exposedsurface 45 is coplanar with the longitudinally extending surface 64 ofshoulder 61. As alternatives one or more of the exposed surfaces of thecores can be left standing proud of the surrounding longitudinallyextending surface e.g. with a convex exposed surface, or, conversely,one or more exposed cores surfaces can be sunk into the surroundinglongitudinally extending surface, e.g. with a concave exposed surface.While this step has been described as following the preceding step it isof course possible to perform these two steps substantiallysimultaneously.

Subsequently, as shown in FIG. 4 d) a continuous electrically conductingbiocompatible coating 47 can be applied to the exposed surface of saidhelix body precursor so that it covers the insulating sheath, shoulders59, 61 and the exposed surfaces 43, 45 of the electrically conductingcores 37, 39.

Finally, as shown in FIGS. 4 e) and 4 f) a continuous loop 71, resp. 73of said electrically conducting biocompatible coating 47 on theinsulating sheath surrounding each of the exposed surfaces 43, 45 of theelectrically conducting cores 37, 39 is removed. The result of this isthat each electrically conducting coating on the exposed surface 43, 45of each core 37, 39 is not in electrical contact with the remainingelectrically conducting coating 47 on said insulating sheath. Thislimits the electrically-effective surface area of each exposed coresurface which will subsequently be used as sensing or stimulatingelectrodes. The biocompatible coating can be removed by, for example,cutting, polishing, grinding or similar methods. The elongated helixbody precursor can now be formed into a helical shape comprising aninternal lumen by winding around a cylindrical former or by any otherknown way in order to form a helix body comprising a plurality ofrevolutions separating a distal end and a proximal end. Preferably theforming of the helical shape is performed so that the exposed surface ofeach core is orientated in a predetermined direction, for exampletowards the exterior of the helix. As in this embodiment of the presentinvention the forming of the helix revolutions takes place after theelectrically conducting biocompatible coating has been applied to theinsulating sheath, it is preferable that the bonding of thebiocompatible coating to the underlying sheath and exposed surface ofthe electrically conducting core is sufficiently strong that thebiocompatible coating is not disturbed or moved during forming of theserevolutions. Examples of coatings which exhibit such strong bonding aretitanium oxide, platinum black, and metal oxides formed from theconducting wire or lead.

FIGS. 5 a)-5 f) show stages in the manufacture of a multi-conductorelectrically active helix in which each conductor has a plurality ofactive electrode in accordance with the above first embodiment of amethod for producing an active fixation means. In these figures thereference numerals used in FIGS. 4 a)-4 f) have been repeated when theycorrespond to similar features. As can be seen from FIGS. 5 a)-5 f) thestages in this method are substantially the same as those describedabove except that in the third step, as shown in FIG. 5 c), a pluralityof cuts are made in the insulating sheath and insulating materialremoved from between alternating pairs of cuts in order to form slits42′, 42″, 42″, resp. 44′, 44″, 44′″ which expose a plurality oflongitudinally extending surfaces 43′, 43″, 43″ of the firstelectrically conducting core 37, resp. a plurality of longitudinallyextending surfaces 45′, 45″, 45″′ of the second electrically conductingcore 39. In this embodiment of the present invention exposed portions offirst core 37 nearest the distal end 55 of the helix body precursor 51are not levelled, i.e. the exposed surfaces 43′, 43″, 43″′ project abovethe longitudinally extending surfaces 62 of the slits 42′, 42″, 42″′formed in shoulder 59. Similarly the exposed portions of second core 39nearest the distal end 55 of the helix body precursor 51 are notlevelled, i.e. the surfaces of its exposed surfaces 45′, 45″, 45″′project above the longitudinally extending surfaces 64 of the slits 44′,44″, 44″′ formed in shoulder 61. As alternatives one or more of theexposed surfaces 43′-43″′, 45′-45″′ of the cores can made level with thesurrounding longitudinally extending slit's surface or, one or moreexposed cores surfaces can be sunk into the surrounding longitudinallyextending slit's surface, e.g. with a concave exposed surface. Whilethis step has been described as following the preceding step it is ofcourse possible to perform these two steps substantially simultaneously.

Subsequently, as shown in FIG. 5 d) a continuous electrically conductingbiocompatible coating 47 can be applied to the exposed surface of saidhelix body precursor so that it covers the insulating sheath, shoulders59, 61 and the exposed surfaces 43′-43″′, 45′-45″′ of the electricallyconducting cores 37, 39.

Finally, as shown in FIGS. 5 e) and 5 f) a continuous loop 71′-71″′,resp. 73′-73″′ of said electrically conducting biocompatible coating 47on the insulating sheath surrounding each of the exposed surfaces43′-43″′, 45′-45″′ of the electrically conducting cores 37, 39 isremoved. The result of this is that each electrically conducting coatingon the exposed surfaces of each core 37, 39 is not in electrical contactwith the remaining electrically conducting coating 47 on said insulatingsheath. This limits the electrically-effective surface area of eachexposed core surface which will subsequently be used as sensing orstimulating electrodes. The biocompatible coating can be removed by, forexample, cutting, polishing, grinding or similar methods. The elongatedhelix body precursor can now be formed into a helical shape comprisingan internal lumen by winding around a cylindrical former or by any otherknown way in order to form a helix body comprising a plurality ofrevolutions separating a distal end and a proximal end. Preferably theforming of the helical shape is performed so that the exposed surface ofeach core is orientated in a predetermined direction, for exampletowards the exterior of the helix.

In a second embodiment of a method for producing an active fixationmeans in the form of an electrically active helix, the helix bodyprecursor is formed into a helical shape before the surfaces of theconducting core or cores are exposed. Thus this method is similar to thefirst embodiment of the invention except that the forming of the helixis performed before the application of coatings. In more detail anexample of a second embodiment of the present invention comprises thesteps of:

a) forming a helix body having a proximal end and a distal end connectedby a plurality of helical revolutions, said body comprising at least oneelectrically conducting core partially surrounded by an insulatingsheath whereby a continuous portion of the surface of each electricallyconducting core extending from said distal end towards said proximal endand facing in a predetermined direction is exposed;

b) applying a continuous electrically conducting, biocompatible coatingto surface of said insulating sheath and each exposed surface of eachelectrically conducting core;

c) removing a portion of said electrically conducting biocompatiblecoating on the insulating sheath surrounding each continuous portion ofthe surface of each electrically conducting core such that theelectrically conducting coating on the exposed surface of eachelectrically conducting core is not in electrical contact with theremaining electrically conducting coating on said insulating sheath.

In the above examples, the exposed surfaces 43-45′″ and 45-45″′ whichare to act as sensing or stimulating electrodes are quadratic when seenfrom a view perpendicular to the exposed surface and extendlongitudinally, but it conceivable for them to made in any shape.

There are several possible ways of forming an elongated helix bodyprecursor. For example, as shown in FIGS. 6 a) and 6 b) a electricallyconducting core 81 and an insulating sheath 83 can be extrudedsimultaneously, the insulating sheath 83 being formed with alongitudinal slit 85 such that a continuous longitudinally extendedportion of the surface 87 of said electrically conducting core 81 isexposed and not surrounded by said insulating sheath 83.

Such an elongated helix body precursor can be formed into a helix 89 asshown in FIG. 6 c), for example by winding around a former. The completehelix 89 can then be coated with a biocompatible conductive material 91such as titanium nitride by, for example, vapour deposition as shown inFIG. 6 d). In order to isolate the exposed surface 87 of the core 81which is intended to be electrically active during use from the surfaceof the insulating sheath 83 which is intended to be inactive during use,continuous strips 93 of the biocompatible conductive material 91 on theinsulating sheath 83 can be removed, by polishing, cutting or othersuitable methods, leaving a continuous non-conducting gap 93 between thecore 85 and the major part of the visible surface of the insulatingsheath, as can be seen in FIG. 6 e).

FIGS. 7 a)-7 c) show schematically examples of further possible helixbody precursors in cross-section. FIG. 7 a) shows a cross-sectionthrough a co-extruded or co-formed precursor body 101 containing twosymmetrically-positioned conducting cores 103, 105 of circularcross-section surrounded by a circular insulating sheath 107.

FIG. 7 b) shows a cross-section through a co-extruded or co-formedprecursor body 109 containing three conducting cores 111, 113, 115 eachof circular cross-section surrounded by a circular insulating sheath117. The cores are arranged with the two cores positioned at 90° eitherside of a middle core—thereby leaving a gap of approximately 180° ofinsulating material without any cores. Preferably this gap is arrangedto be facing towards the interior of the helix when the precursor isformed into a helix.

FIG. 7 c) shows a cross-section through a co-extruded or co-formedprecursor body 119 containing an asymmetrically-positioned core 121 ofquadratic cross-section positioned inside an insulating sheath 125 ofC-shaped cross-section, with a surface 125 of core 121 exposed.

The above suggested cross-sections are merely examples of conceivablecross-sections—the skilled person would understand that in the eventthat a lead, precursor body or helix has a plurality of conductors it isalways possible to remove selectively insulating material inpredetermined positions so that when in use in a patient conductors cancome into contact with tissue and thereby be used as a stimulatingand/or sensing electrode.

1. A method of fabricating an electrically active helix for anelectrical medical lead comprising: a) forming a helix body having aproximal end and a distal end connected by a plurality of helicalrevolutions, the helix body comprising at least one electricallyconducting core partially surrounded by an insulating sheath, wherein aportion of a surface of each electrically conducting core extending fromthe distal end towards the proximal end and facing in a predetermineddirection is exposed; b) applying a continuous electrically conducting,biocompatible coating to a surface of the insulating sheath and eachexposed surface of each electrically conducting core; and c) removing aportion of the electrically conducting biocompatible coating on theinsulating sheath surrounding each continuous portion of the surface ofeach electrically conducting core such that the electrically conductingcoating on the exposed surface of each electrically conducting core isnot in electrical contact with the remaining electrically conductingcoating on the insulating sheath.
 2. The method of claim 1, wherein stepa) comprises: i) forming an elongated helix body precursor having aproximal end and a distal end, the helix body precursor comprising atleast one electrically conducting core and a surrounding insulatingsheath in which there is at least one longitudinally extending slit inthe insulating sheath which exposes a portion of each electricallyconducting core; and ii) forming the elongated helix body precursor in ahelix body in which a plurality of helical revolutions are formedbetween the proximal end and the distal end of the helix body precursor,and wherein the exposed surface of each electrically conducting corefaces in a predetermined direction.
 3. The method of claim 2, whereinstep i) comprises the step of forming at least one electricallyconducting core surrounded by an insulating sheath which leaves at leastone portion of each electrically conducting core exposed.
 4. The methodof claim 2 wherein, in step c) the removal of the portion ofelectrically conducting biocompatible coating is achieved by polishingor cutting or grinding or a combination thereof.
 5. The method of claim1, wherein the biocompatible coating is TiN or TiSiC or platinum blackor a metal oxide or other electrically conducting material.